This invention relates generally to removable cover plate constructions for installation in the decks of boats, and more particularly to constructions employing threaded cover plates which can be readily installed or removed to provide quick access to areas below the deck such as a storage space, the bilge, and areas where shut-off valves, instruments, and the like are located. Where such plates were employed with instrument gauges, the plates were sometimes constituted of transparent material such that the gauges could be read with the cover plate still in place.
In the past a number of deck cover constructions employing a deck fitting and a cooperable closure member have been proposed and produced, and have met with varying degrees of success. Several problems were encountered, however, with the prior art constructions. Where the closure member and the deck fitting had cooperable threads of conventional construction, there was a likelihood of binding of the two parts in the event that either became warped. When the parts were constituted of molded plastic, a limited amount of such warping was inevitable as the plastic cured. The deck fitting part, being generally of annular configuration, sometimes assumed a slightly egg-shaped configuration, causing interference or a poor fit between the threads, and resulting in binding as the closure member was screwed in place.
The deck fitting part usually had an apertured annular mounting flange by which it could be screwed in place on the deck. In the event that the latter was not perfectly flat or planar, but instead slightly skewed, the fitting tended to follow this contour, thereby assuming a bowed configuration. This also caused interference problems with the cooperable threads. In addition, it was usually considered important to provide a good sealing surface on the closure part that was engageable with the cooperable surfaces of the deck fitting. When the latter was bowed, such surfaces did not meet uniformly at all points around the periphery of the closure, resulting in a poor fit and the likelihood of leakage of water past the cover and into the area beneath the deck.
There were also cost disadvantages involved in providing, on such fittings, threads extending beyond 360.degree. in spiral circumference, since the provision of such threads made molding of the parts difficult. A suitable location for a parting line in a pair of mold cavities is often difficult or impossible to find when it is desired to mold each of the parts in a single step or operation. In addition, where relatively small gauge threads were involved, there was a likelihood of large grains of sand or dirt becoming lodged in the areas around the threads, resulting in undesirable binding or seizing thereof.